1. Field of the Invention
The present invention relates to an optical window contamination detecting device for an optical apparatus such as an imaging apparatus for deflection scanning light with a mirror, irradiating with the light a measuring space outside the apparatus to acquire a one-dimensional image from an intensity of reflected light from an object, and a light wave distance measuring apparatus for measuring a distance based on delay time between modulated measurement light and reflected light from an object.
2. Description of the Related Art
As shown in FIG. 8, there is proposed a scanning type distance measuring apparatus 100 accommodating, in a casing 101 formed with an optical window 102, a light transmitting unit 3, a scanning mechanism 4 for deflection scanning measurement light output from the light transmitting unit 3 into a measuring space through the optical window 102, and a light receiving unit 5 for detecting reflected light from an object X through the optical window 102.
The above-described distance measuring apparatus is used in a visual sensor of a robot or an automatic guided vehicle, an opening/closing sensor of a door, a monitoring sensor for detecting presence of an intruder to a monitoring region, a safety sensor for detecting a person or an object approaching a dangerous machine to safely stop the machine, and the like.
Furthermore, the distance measuring apparatus may also be used to recognize a shape of a vehicle or a human, and for example, may be used as a sensor for discriminating a vehicle type and counting the number of passing cars in the ETC system, or a monitoring sensor for counting the number of people and detecting flow of the people.
However, when the optical window 102 becomes contaminated with mud, water droplets, or the like, there arises a serious problem that the distance measuring function cannot be appropriately exhibited, such as an appropriate amount of light is not irradiated, and the light reflected by the object X is not detected.
Therefore, it is required a function of constantly monitoring even microscopic contamination instantaneously attached to the optical window arranged in a wide range in correspondence to a scanning range of the measurement light, and outputting an abnormality signal or a failure signal if the contamination significantly affects performance of the apparatus to safely stop the apparatus.
As a contamination detecting device of an optical window, a laser distance measuring device is proposed in U.S. Pat. No. 5,455,669 in which an optical window 41 is arranged in a curved form in an outer peripheral direction of the device so as to be inclined from a vertical direction, and a plural sets of light transmitting/receiving elements each including a light transmitting element 91 arranged on a lower side and a light receiving element 92 arranged on a upper side of the optical window 41, the sets of light transmitting/receiving elements for detecting contamination on the optical window 41 existing along optical paths 98, are arranged side by side along the optical window 41, as shown in FIG. 10A.
Japanese Laid-Open Patent Publication No. 10-90412 proposes an object information detection device for irradiating light with a light transmitting element 25 from an inner side of an optical window 2 and detecting with a light receiving element 29 the light double refracted by one part of the optical window 2 to detect contamination on the optical window 2, as shown in FIG. 10B.
However, in the technique described in the U.S. Pat. No. 5,455,669, there arise new problems such as adjustment of an optical axis of each light transmitting/receiving element and prevention of interference between the light transmitting/receiving elements arranged side by side, since a great number of light transmitting/receiving elements must be arranged side by side at small intervals to detect the entire region of the optical window without any blind spots when it is necessary to detect minor contamination. Furthermore, the number of components increases and thus the device becomes expensive.
In the technique described in Japanese Laid-Open Patent Publication No. 10-90412, the device can be configured more compact than that described in Patent Publication No. 5,455,669, but has a problem in that, when water droplets attach to a reflecting surface of a case, judgment is sometimes mistakenly made if the light is reflected diffusely by the water droplets and detected by the measurement light receiving element, and also has another problem in that a great number of light transmitting/receiving elements are required similarly to the above-described case when it is necessary to detect minor contamination on the optical window.